As the primary inhibitory neurotransmitter in mammalian brain, GABA, its content and its receptor systems are the targets of a number of anti-epileptic drugs. Although Petroff and colleagues have studied the effects of various anti-epileptics on brain GABA levels in the occipital lobe, a site distant from the epileptogenic region, to date little information exists regarding GABA levels in the epileptogenic region of patients with temporal lobe epilepsy. This data has largely shown that brain GABA levels are decreased in patients with poor control in comparison to healthy controls and are responsive to a variety of anti-epileptic medications. Conversely, recent preliminary microdialysis studies have shown that ECF GABA is higher in patients with sclerosis as opposed to those without sclerosis (6). Additionally our preliminary data has shown a similar correlation with ECF GABA inversely correlated with hippocampal NAA levels (i.e higher ECF GABA levels are seen in patients with lower NAA levels. To what extent total GABA in the epileptogenic region is increased or decreased relative to control is unknown. Similarly it is unknown if total GABA levels in the epileptogenic parallel GABA levels distant from the seizure focus. Clearly these questions may have significant impact on our understanding of the factors leading to epileptogenic activity in the seizure focus and also provide measures that may aid in the therapeutic management of epilepsy patients. Therefore the development of robust methods for measuring GABA from the temporal lobe in patients with temporal lobe epilepsy would be of significant benefit. [unreadable] [unreadable] [unreadable]